1. Technical Field
The invention first relates to a transport device in accordance with the preamble of claim 1.
2. Prior Art
A transport apparatus of the type according to the species is known, for example, from JP 06306691 A, or also from DE 84 22 297 U1.
The subject of DE 84 22 297 U1 is essentially concerned with assuring the widest possible opening of the clamp-like lower pickup area in order to make possible an automatic or robot-like equipment of the transport device with printed circuit plates. To this end one leg of the clamp-like pickup area is embodied to be stationary, the other is fastened on a turntable, on which a vertically displaceable element, which in this embodiment is constituted by a spring-loaded piston rod, acts via a cam connection. When the piston rod is actuated by an external force, for example pneumatically, the turntable pivots the movable leg aside.
This geometry is extremely disadvantageous since, because of the predetermined lever ratio between the radius of the turntable on the one side and the distance of the pickup area for the printed circuit boards from the turning point of the turntable on the other side, only relatively weak holding forces can be exerted on the printed circuit boards, or the "particularly good clamping effect of the tongs", also desired in connection with the subject of this reference, can only be achieved with a very high spring force, which requires a correspondingly elaborate mechanical construction, as well as a very high actuation force as the counter-force to this spring for opening the tongs.
When establishing a transport system with a plurality of such transport devices, the latter are suspended on a support rail by means of a strap; accordingly, the large actuation force for opening the tongs requires elaborate and mechanically solid actuation devices on the support rail.
JP 06306691 A employs a rocker-like mechanism for opening and closing the clamp-like pickup area, wherein also a stationary leg and a gripping leg, seated in a rocker-like manner, are provided. The piston rod of an essentially vertically maintained cylinder acts on the upper end of this gripping leg via an elaborate mechanical rod system. The holding power of this clamping device is exclusively determined by a spring held between the two upper ends of the clamps, wherein the achievable holding force of this known device can be a multiple of the spring force because of an appropriately selected rocker-like seating. The piston rod must be retracted into the cylinder for opening the clamp, and the clamping rocker is then actuated via the linkage mechanism against the force of the spring. However, this quite compactly embodied transport device has the disadvantage of many hinges and pivot levers, and apparently is intended for the electrical or pneumatic opening/closing of the pickup area. This device is too elaborate and cumbersome for use in a transport system.
U.S. Pat. No. 5,102,287 discloses a similar device which, however, from the beginning is not intended for use with a transport system for chemical or electrolytic surface treatment; here, two symmetrically constructed and rocker-like maintained clamping elements are provided, which have control cams on their surfaces facing each other, on which a vertically operating plunger acts, by means of which the opening and the closing of the two clamps can be accomplished. Because of the design of these control cams it is possible to achieve a relatively large holding force between the ends of the two clamps wherein, however, also because of the disadvantageous selection of the lever arm between the clamp ends on the one side and contact points of the plunger with the clamps, this plunger must be charged with very high forces, which results in a correspondingly elaborate apparatus, as can be seen from the tall construction of the cylinder devices provided there. Therefore such a solution is not usable for employment in transport systems.